Anaplasmosis is a disease caused by a rickettsial parasite of ruminants, Anaplasma spp. The microorganism is gram-negative and occurs in the red blood cells. It is transmitted by natural means through a number of haematophagous species of ticks. Anaplasmosis can also be transmitted by the use of surgical, dehorning, castration, and tattoo instruments and hypodermic needles that are not disinfected between uses. Although the term is often associated with animal infection, it is also used to describe infection in humans.